Has nothing to do with the lighting if the texture is setup incorrectly

I had this trouble with skyboxes before also so I should be able to help you fix it.

the problem is probably with the vmt code so here is a working one that you can take the code from.

also the vmt must have the same name as the vtf

https://www.dropbox.com/s/x3j77u1g99viony/example.vmt

Hmm... interesting. Haven't seen this issue before (it might be the texture file(s), but I'm not sure...). Anyway, it seems you're missing a bottom texture.

Software to have to work well with Hammer : Bspsrc / Pakrat / GCFScape / VTFEdit / Notepad++ ......and more

To decompile a map must : Bspsrc

But tonight at home.......it will be in the afternoon with you

I can help you anymore tonight

Sorry I was wrong file for skybox124
Here is the correct file : http://dl.free.fr/uKbyLvzKq
Password : 5984637
Open the VMT with Notepad++ and VTF with VTFEdit
And look at the specifications

Oh, but there's one teeny problem with the skybox124; the skybox124_dn is the same as the skybox124_up, so instead of seeing the land while looking down, you see the sky, so the bottom part of the skybox is the wrong file. When I look down on your map, I see the ground. Decompilers will not work for me however, so I cannot find the bottom myself. Can you please share the correct skybox124_dn VTF and VMT?

Wow, thank you so much! What changes did you do to the sky textures to make them work? Also, thank you for the skybox124. Is it alright if I use this? What's it from, by the way?

Plus, in this map, I've found my player sinking into the ground while in front of a linked portal. I just discovered that this is due to a portalable surface being connected to a painted-geometry surface, so I will also fix that. I will compile an updated map in 1 week (after my summer Math class finally ends). Again, thank you Sisko_83!

I give you the file.....password is 564231 : http://dl.free.fr/uqtHcqC7I
Do not put anything in the user

here is it works
I do tutorials on Hammer but in French.....sorry
https://www.youtube.com/watch?v=F_xfRsX2OAg&feature=youtu.be

I decompile your map and there is nothing good for the skybox.
Must be redone from scratch
Sorry for my bad english

If you want, give me your VFM and I modified it to work

Well that is weird nonetheless, but not surprising. I will study skybox tutorials even more and will work on it in about a week. Thank you for participating in this experiment.

As soon as the map spawns the texture is flickering.

So then, everything is fine until a Portal lands, right?

Kinda, sorta, yes and no. It flickers in and out from sky texture to black. When I look around it makes it flicker in and out.